Observations on 7416 Canadian Holstein cows were examined to estimate genetic parameters for the most common diseases of dairy cows. Mastitis, ovarian cyst, ketosis, milk fever, abomasal displacement, and culling that is due to reproductive failure or leg problems were analyzed as binomial traits, assuming an underlying threshold model that included fixed and random effects. Sire and residual components of variance were estimated by REML to provide heritability estimates from paternal half-sibs. A multiple-trait mixed model was also used to estimate genetic and environmental correlations between production and disease traits. Heritabilities of disease traits were relatively low and ranged from 0 to .15, except for displaced abomasum (h2 = .28). Evidence of genetic antagonism existed between incidence of mastitis and milk production. Incidence of milk fever was genetically associated with cows of lower genetic potential for production. Genetic associations between displaced abomasum and production traits were small, and estimates of genetic correlations between ovarian cyst and milk production were inconsistent across lactations. Ketosis was antagonistically associated genetically with production of milk and fat but was favorably associated with production of protein. The long-term cumulative effect of genetic selection against diseases might be useful to diminish their incidence.

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SUMMARY: Most Chilean sheep stock comprises different degrees of crossbreeding over Corriedale breed. A common absorbent crossbreeding has been Australian Merino over Corriedale which, in many cases, has not been complete. The aim of this study was to evaluate the process of morphology differentiation and structural functionality of Corriedale ewes undergoing incomplete absorbent crossbreeding which was carried out in order to create an animal with a new morphology. A total of four hundred adult ewes were measured; two hundred belonging to the incomplete crossbreeding, and two hundred from the two original breeds (one hundred Corriedale and one hundred Australian Merino ewes). All measured ewes were randomly selected. Fourteen body measurements were recorded and nine body indexes were calculated for each ewe. Results show that a new biotype has been created from the absorbent crossbreeding of Corriedale by Australian Merino, which produced ewes with a clear morphological and structural functionality differentiation as compared to the two original breeds. The new body format shows morphostructural variability coefficients that are similar to those found on other formally recognized sheep breeds.

ABSTRACT. Chilean milk processing industry is providing clear signs to milk farmers regarding the significant importance of milk solids within raw milk payment schemes. A litre of milk containing 3% of fat and 3% of protein is defined as a basic litre and, each additional kilo of fat and/or protein receives an extra payment. These are new production traits which must be researched on. In this study, 64,029 lactations, on 24 Región de Los Ríos at Southern of Chile herds, were used. Genetic parameters for milk yield and fat and protein above 3% yield were estimated. A multiple trait linear model, solved by BLUP methodology, was used. Variance components were estimated using AIREMLF90 and VCE software. Estimated heritability for milk yield, and fat and protein above 3% yield were 0.16±0.004, 0.44±0.007 and 0.42±0.006, respectively. Estimated genetic correlations were -0.285 and -0.331 between milk yield and fat and protein above 3% yield, respectively. It is concluded that there exist genetic variation for the two new traits proposed by the Chilean milk processing industry and, genetic selection for these traits should be done based on their estimated breeding values. However these two traits, plus milk yield, should be included in a selection index to account for the negative genetic correlations among them and minimise selection against milk yield.Key words: genetic improvement, milk solids. RESUMEN.En Chile la industria está dando señales claras al productor lechero al otorgar una importante ponderación al contenido de sólidos lácteos en la determinación del precio de la leche cruda. Para este efecto se definió como "litro base" a un litro de leche con contenidos de 3,0% de grasa y 3,0% de proteína. Sobre dicha base, cada kilogramo de ambos sólidos recibe una valoración adicional, constituyéndose así nuevas características composicionales que deben ser estudiadas. En este estudio se estimaron parámetros genéticos para producción de leche y producción de grasa y proteína sobre 3% de concentración en leche, a partir de 64.029 lactancias provenientes de 24 rebaños de la Región de Los Ríos en el sur de Chile. Se utilizó un modelo mixto multivariado resuelto con metodología BLUP. Los componentes de varianza fueron estimados usando los programas computacionales AIREMLF90 y VCE. Las heredabilidades estimadas para volumen de leche y producción de grasa y proteína sobre el 3,0% fueron 0,16±0,004, 0,44±0,007 y 0,42±0,006, respectivamente. Las correlaciones genéticas entre producción de leche y producción de grasa y proteína sobre 3% fueron -0,285, -0,331, respectivamente. Se concluye que existe variabilidad genética para las dos nuevas características creadas por la industria compradora de leche y que la selección genética debería hacerse basada en valores genéticos estimados para estas.Palabras clave: mejoramiento genético, sólidos, leche.

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